Buildings.HeatTransfer.Functions.ConvectiveHeatFlux

Correlations for convective heat flux

Information


This package contains functions for the convective heat transfer.
Input into the functions is the temperature difference between 
the solid and the fluid. 
The functions compute the convective heat flux, rather than the 
convective heat transfer coefficient.
The reason is that the convective heat transfer coefficient
is not differentiable around zero for certain flow configurations,
such as buoyancy driven flow at a horizontal surface. However, the
product of convective heat transfer coefficient times temperature 
difference is differentiable around zero.

Package Content

NameDescription
Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.BaseClasses BaseClasses Base classes for convective heat transfer coefficients
Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.constantCoefficient constantCoefficient Constant convective heat transfer coefficient
Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.wall wall Free convection, wall
Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.floor floor Free convection, floor
Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.ceiling ceiling Free convection, ceiling


Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.constantCoefficient

Constant convective heat transfer coefficient

Information


This function computes the convective heat transfer coefficient as
h=hCon, where hCon=3 is a default input argument.
The convective convective heat flux is then
q_flow = h * dT,
where dT is the solid temperature minus the fluid temperature.

Extends from Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.BaseClasses.PartialConvectiveHeatFlux (Partial function for convective heat flux).

Inputs

TypeNameDefaultDescription
TemperatureDifferencedT Temperature difference solid minus fluid [K]
CoefficientOfHeatTransferhCon3Constant for convective heat transfer coefficient [W/(m2.K)]

Outputs

TypeNameDescription
HeatFluxq_flowConvective heat flux from solid to fluid [W/m2]

Modelica definition

function constantCoefficient 
  "Constant convective heat transfer coefficient"
  extends Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.BaseClasses.PartialConvectiveHeatFlux;
  input Modelica.SIunits.CoefficientOfHeatTransfer hCon = 3 
    "Constant for convective heat transfer coefficient";
algorithm 
  q_flow :=hCon*dT;
end constantCoefficient;

Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.wall

Free convection, wall

Information


This function computes the buoyancy-driven convective heat transfer coefficient 
for a wall as
h=1.3*|dT|^0.3333,
where dT is the solid temperature minus the fluid temperature.
The convective convective heat flux is then
q_flow = h * dT.

Extends from Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.BaseClasses.PartialConvectiveHeatFlux (Partial function for convective heat flux).

Inputs

TypeNameDefaultDescription
TemperatureDifferencedT Temperature difference solid minus fluid [K]

Outputs

TypeNameDescription
HeatFluxq_flowConvective heat flux from solid to fluid [W/m2]

Modelica definition

function wall "Free convection, wall"
  extends Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.BaseClasses.PartialConvectiveHeatFlux;
algorithm 
  q_flow := sign(dT)*1.3*abs(dT)^1.3333;

end wall;

Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.floor

Free convection, floor

Information


This function computes the buoyancy-driven convective heat transfer coefficient 
for a floor as
h=k*|dT|^0.3333,
where 
k=1.51 if the floor is warmer than the fluid,
or k=0.76 otherwise, and where
dT is the solid temperature minus the fluid temperature.
The convective convective heat flux is then
q_flow = h * dT.

Extends from Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.BaseClasses.PartialConvectiveHeatFlux (Partial function for convective heat flux).

Inputs

TypeNameDefaultDescription
TemperatureDifferencedT Temperature difference solid minus fluid [K]

Outputs

TypeNameDescription
HeatFluxq_flowConvective heat flux from solid to fluid [W/m2]

Modelica definition

function floor "Free convection, floor"
  extends Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.BaseClasses.PartialConvectiveHeatFlux;

algorithm 
  q_flow  := if (dT>0) then 1.51*dT^1.3333 else -0.76*(-dT)^1.3333;
end floor;

Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.ceiling

Free convection, ceiling

Information


This function computes the buoyancy-driven convective heat transfer coefficient 
for a ceiling as
h=k*|dT|^0.3333,
where 
k=1.51 if the fluid is warmer than the ceiling,
or k=0.76 otherwise, and where
dT is the solid temperature minus the fluid temperature.
The convective convective heat flux is then
q_flow = h * dT.

Extends from Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.BaseClasses.PartialConvectiveHeatFlux (Partial function for convective heat flux).

Inputs

TypeNameDefaultDescription
TemperatureDifferencedT Temperature difference solid minus fluid [K]

Outputs

TypeNameDescription
HeatFluxq_flowConvective heat flux from solid to fluid [W/m2]

Modelica definition

function ceiling "Free convection, ceiling"
  extends Buildings.HeatTransfer.Functions.ConvectiveHeatFlux.BaseClasses.PartialConvectiveHeatFlux;

algorithm 
   q_flow  := if (dT>0) then 0.76*dT^1.3333 else -1.51*(-dT)^1.3333;
end ceiling;

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